Hoist and winch cable angle sensor

ABSTRACT

An assembly includes a hoist or a winch, a cable, and a fleet angle sensor. The fleet angle sensor includes a frame disposed around an opening. A first photodetector with multiple light-receiving zones is mounted on the frame. A first light source is mounted on the frame opposite the first photodetector. The first light source directs a first light beam across the opening to the multiple light-receiving zones of the first photodetector. The cable extends through the opening and into the first light beam, and the multiple light-receiving zones produce signals that vary based upon a fleet angle of the cable extending through the opening.

BACKGROUND

Hoist and winches are commonly used on helicopters and ships to haul,pull, raise, and lower heavy loads. Winches include a drum that supportsa spool of cable that runs to the load, usually through one or moresheaves. The cable may be formed of steel or rope depending upon the useand environment of the winch. The winch spools and unspools the cable byrotating the drum. As the cable is taken in it is spooled onto the drumin multilayers. Cable or hoist/winch damage could occur as the cable isspooled if the fleet angle between the cable and the spool axis becomestoo large, causing the cable to drag over adjacent wraps. Excessivefleet angle can also induce severe safety concern to the helicopter ifthe cable tangles with the body of the helicopter. External forces canalso damage the hoist and winches if its fleet angle is too large. Suchexternal forces could include wind, drag as the load at the end of thecable is pulled through water, or forces caused by the motor as themotor spools and unspools the cable.

Fleet angle is the angle between the center axis of alignment and thecable. Generally the center axis of alignment is defined as the axiswhere the cable would hang straight down if no other force other thangravity were acting upon it. By maintaining an acceptable fleet angle,the drum of the winch can spool the cable without causing the cable todrag over and wear adjacent wraps. In the past, a mechanical trackingdevice referred to as a follower has been used to guide the cable as thecable is spooled and unspooled. However, followers are prone to smalltiming errors that accumulate as the cable changes in diameter over timeand use. The fleet angle of the cable may also be controlled throughdrum controls that vary the rotational speed of the drum, but the drumcontrols require sensors that are able to provide accurate, real-timemeasurements of the fleet angle of the cable.

In some applications, obtaining accurate, real-time measurements of thefleet angle of the cable is challenging because the cable is constantlyvibrating, swaying, or bouncing. One such application is sonar dipping.In sonar dipping, a winch is mounted to a helicopter. The winch lowersan electric supporting cable with a specialized sonar for submersion inwater to detect the presence of submarines. To take measurements atspaced intervals, the winch repeatedly raises and lowers the sonar athigh speeds averaging about five meters per second. Because of the rapidand erratic movement of the cable, there is a need for a fleet anglesensor with high resolution and fast response time to accurately measurethe fleet angle of the cable.

SUMMARY

In one aspect of the invention, an assembly includes a winch, a cable,and a fleet angle sensor. The fleet angle sensor includes a framedisposed around an opening. A first photodetector with multiplelight-receiving zones is mounted on the frame. A first light source ismounted on the frame opposite the first photodetector. The first lightsource directs a first light beam across the opening to the multiplelight-receiving zones of the first photodetector. The cable extendsthrough the opening and into the first light beam, and the multiplelight-receiving zones produce signals that vary based upon a fleet angleof the cable extending through the opening.

In another aspect of the invention, a method for measuring the fleetangle of a cable includes directing a first light beam across an openingto a first photodetector, the first photodetector having a firstlight-receiving zone and a second light receiving zone. A cable ispassed through the opening and across a portion of the first light beam.The light received by the first light-receiving zone is measured and thelight received by the second light-receiving zone is measured. A lightmeasurement of the first light-receiving zone is compared to a lightmeasurement of the second light-receiving zone to calculate a firstcoordinate of the cable.

In another aspect of the invention, an angle sensor includes a frame anda first light source disposed on the frame. A first quadrant photodiodeis disposed on the frame opposite the first light source. A second lightsource is disposed on the frame and a second quadrant photodiode isdisposed on the frame opposite the second light source. A circuitdetermines the angular orientation of a cable passing through the framebased on signals from the first and second quadrant photodiodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a helicopter with a cable winch.

FIG. 2 is a cross-sectional view of a fleet angle sensor and sheavesfrom the cable winch of FIG. 1.

FIG. 3 is a perspective cross-sectional view of the fleet angle sensorfrom FIG. 2.

FIG. 4 is a cross-sectional view of the fleet angle sensor from FIG. 3taken along line AA.

FIG. 5A is a front view of a first photodetector from the fleet anglesensor of FIG. 4 and a cable with a fleet angle of zero.

FIG. 5B is a front view of the first photodetector from FIG. 5A and thecable with a fleet angle greater than zero.

FIG. 5C is another front view of the first photodetector from FIG. 5Aand the cable with a fleet angle greater than zero.

FIG. 6A is a front view of a second photodetector from the fleet anglesensor of FIG. 4 and the cable with a fleet angle of zero.

FIG. 6B is a front view of the second photodetector from FIG. 6A and thecable with a fleet angle greater than zero.

FIG. 6C is another front view of the second photodetector from FIG. 6Aand the cable with a fleet angle greater than zero.

FIG. 7 is a schematic diagram of the first photodetector from FIG. 5Aand a first circuit associated with the first photodetector.

FIG. 8 is a schematic diagram of the second photodetector from FIG. 6Aand a second circuit associated with the second photodetector.

DETAILED DESCRIPTION

The present invention provides a fleet angle sensor with fast responsetime and high enough resolution to measure the fleet angle of a cablewithin one tenth of a degree. The fleet angle sensor includes a framewith an opening for receiving the cable, a quadrant photodiode mountedon the frame, and a light source mounted on the frame to direct a lightbeam across the opening to the quadrant photodiode. The quadrantphotodiode is connected to a circuit that determines the fleet angle ofthe cable based on signals from the quadrant photodiode.

FIG. 1 is a side view of helicopter 10 with winch assembly 12 supportingload 14. As shown in FIG. 1, winch assembly 12 includes winch 16, cable18, and fleet angle sensor 20. Winch 16 is mounted to helicopter 10 andraises and lowers load 14 by taking in or paying out cable 18. ThoughFIG. 1 shows load 14 as a dipping sonar, load 14 may include any objectconnected to cable 18 and moved by winch 16. Fleet angle sensor 20 isconnected below winch 16. As discussed below in FIG. 2, cable 18 passesthrough fleet angle sensor 20 so that fleet angle sensor 20 may measurethe fleet angle of cable 18.

FIG. 2 is a cross-sectional view of sheaves 22 and fleet angle sensor 20from winch assembly 12 of FIG. 1. As shown in FIG. 2, winch assembly 12includes cable 18, fleet angle sensor 20, and sheaves 22. Fleet anglesensor 20 includes frame 24, opening 26, first photodetector 28, firstlight source 30, first light beam 32, first lens 34, and second lens 36.Maximum angle range 38 defines the full range of cable 18 on the x-axisrelative to the z-axis. Frame 24 includes annular ring 40, outercircumferential surface 42, inner circumferential surface 44, topsurface 46, bottom surface 48, first bore 50, and second bore 52. Fleetangle sensor 20 may also include shield device 51 with bristles 53 andinside surface 55.

Cable 18 passes between sheaves 22 before passing across fleet anglesensor 20 through opening 26. Sheaves 22 center cable 18 above fleetangle sensor 20 such that cable 18 is collinear with a center axis offleet angle sensor 20 when frame 24 is horizontal and no other forceother than gravity is acting upon cable 18. Sheaves 22 also preventcable 18 from rubbing against frame 24 of fleet angle sensor 20 bydefining a pivot point of cable 18 just above fleet angle sensor 20.Frame 24 of fleet angle sensor 20 is disposed around opening 26 formingannular ring 40 with outer circumferential surface 42, innercircumferential surface 44, top surface 46 and bottom surface 48. Innercircumferential surface 44 is several times larger in diameter thancable 18 so that opening 26 is sufficiently large to accommodate maximumangle range 38 of cable 18. Maximum angle range 38 is the maximum fleetangle that cable 18 is likely to experience on any side of the centeraxis of fleet angle sensor 20. As shown in FIG. 2, the maximum fleetangle that cable 18 is likely to experience is fifteen to twenty degreesfrom the center axis of fleet angle sensor 20. First bore 50 extendsthrough outer circumferential surface 42 and inner circumferentialsurface 44 of frame 24. Second bore 52 also extends through outercircumferential surface 42 and the inner circumferential surface 44opposite first bore 50 and is diametrically aligned with first bore 50.

First photodetector 28 is disposed on outer circumferential surface 42over first bore 50, and first light source 30 is disposed on outercircumferential surface 42 over second bore 52 opposite firstphotodetector 28. First light source 30 directs first light beam 32through second bore 52, across opening 26, and through first bore 50 tofirst photodetector 28. First light source 30 may be a laser, LED, diodelaser, infrared emitter, ultraviolet emitter, incandescent bulb, or anyother instrument capable of generating light. Cable 18 intersects firstlight beam 32, and as cable 18 moves and shifts within opening 26, theintensity of first light beam 32 on first photodetector 28 changes andfirst photodetector 28 produces signals representative of the intensitychanges in first light beam 32. As discussed in greater detail belowwith reference to FIGS. 5A-7, first photodetector 28 is a quadrantphotodiode with multiple light-receiving zones. The multiplelight-receiving zones together detect the changes in first light beam 32caused by cable 18 to determine the location of cable 18 within opening26 and a fleet angle of cable 18. First light beam 32 is larger indiameter than cable 18 so that cable 18 never fully blocks first lightbeam 32 from first photodetector 28. Second lens 36 may be disposed insecond bore 52 to collimate first light beam 32. In the case where firstlight source 30 is the same size or smaller in diameter than cable 18,second lens 36 may be a projection lens to enlarge first light beam 32to make first light beam 32 larger in diameter than cable 18. Becausefirst light beam 32 is larger in diameter than cable 18, second bore 52also is larger in diameter than cable 18 to accommodate first light beam32. First lens 34 may be disposed in first bore 50 to collimate firstlight beam 32 before it contacts first photodetector 28. In the casewhere first lens 34 only collimates first light beam 32, firstphotodetector 28 is larger in diameter than cable 18 so that cable 18never fully shadows first photodetector 28 from first light beam 32.First photodetector 28 may be smaller in diameter than cable 18 whenfirst lens 34 is a collection lens larger in diameter than cable 18. Asa collection lens, first lens 34 focuses first light beam 32 onto firstphotodetector 28 where first photodetector 28 detects changes in focusedfirst light beam 32. Because first photodetector 28 or first lens 34must be larger in diameter than cable 18 to prevent cable 18 from fullyshadowing first photodetector 28 from first light beam 32, first bore 50also is larger than cable 18 to accommodate first photodetector 28 andfirst lens 34. As described below in FIGS. 3 and 4, second photodetector54 and second light source 56 may be disposed on frame 24.

Shield device 51 is disposed under frame 24 proximate bottom surface 48of frame 24 and blocks ambient light, water, dirt, and othercontaminants from entering opening 26 and interfering with fleet anglesensor 20. Bristles 53 extend from inside surface 55 of shield device 51towards the center axis of fleet angle sensor 20. Bristles 53 may bearranged in multiple layers so as to block ambient light from enteringopening 26. As winch assembly 12 takes in or pays out cable 18, cable 18rubs against bristles 53 to remove water, dirt, or other contaminantsthat may be present on cable 18. Bristles 53 are flexible such thatbristles 53 contact cable 18 without restricting the motion of cable 18.While shield device 51 has been described as including bristles 53 toblock light, water, dirt, and other contaminants from entering opening26, shield device may employ other means to block contaminants fromentering opening 26, such as a flexible diaphragm with a hole toaccommodate cable 18.

FIG. 3 is a perspective cross-sectional view of fleet angle sensor 20from FIG. 2. FIG. 4 is a cross-sectional view of fleet angle sensor 20from FIG. 3 and cable 18 taken along line AA. As shown in FIGS. 3 and 4,fleet angle sensor includes frame 24, opening 26, first photodetector28, first light source 30, first light beam 32, first lens 34, secondlens 36, second photodetector 54, second light source 56, second lightbeam 58, third lens 60, and fourth lens 62. Frame 24 includes annularring 40, outer circumferential surface 42, inner circumferential surface44, top surface 46, bottom surface 48, first bore 50, second bore 52,third bore 64, and fourth bore 66.

In FIGS. 3 and 4, components of like numbering with the components ofFIG. 2 are assembled as discussed above with reference to FIG. 2. Thirdbore 64 extends through outer circumferential surface 42 and innercircumferential surface 44 of frame 24. Fourth bore 66 also extendsthrough outer circumferential surface 42 and the inner circumferentialsurface 44 opposite third bore 64 and is diametrically aligned withthird bore 64. Third bore 64 and fourth bore 66 are circumferentiallypositioned on frame 24 ninety degrees from first bore 50 and second bore52. Second photodetector 54 is disposed on outer circumferential surface42 over third bore 64, and second light source 56 is disposed on outercircumferential surface 42 over fourth bore 66 opposite secondphotodetector 54. First light source 30 is circumferentially positionedon frame 24 ninety degrees from second light source 56, and firstphotodetector 28 is circumferentially positioned on frame 24 ninetydegrees from second photodetector 54. Second light source 56 directssecond light beam 58 through fourth bore 66, across opening 26, andthrough third bore 64 to second photodetector 54. Similar to first lightsource 30, second light source 56 may be a laser, LED, diode laser,infrared emitter, ultraviolet emitter, incandescent bulb, or any otherinstrument capable of generating light. Cable 18 intersects second lightbeam 58, and as cable 18 moves and shifts within opening 26, theintensity of second light beam 58 on second photodetector 54 changes andsecond photodetector 54 produces signals representative of the intensitychanges in second light beam 58. As discussed in greater detail belowwith reference to FIGS. 6A-8, second photodetector 54 is a quadrantphotodiode with multiple light-receiving zones. The multiplelight-receiving zones together detect the changes in second light beam58 caused by cable 18 to determine the location of cable 18 withinopening 26 and a fleet angle of cable 18. Second light beam 58 is largerin diameter than cable 18 so that cable 18 never fully blocks secondlight beam 58 from second photodetector 54. Fourth lens 62 may bedisposed in fourth bore 66 to collimate second light beam 58. In thecase where second light source 56 is the same size or smaller indiameter than cable 18, fourth lens 62 may be a projection lens toenlarge second light beam 58 to make second light beam 58 larger indiameter than cable 18. Because second light beam 58 is larger indiameter than cable 18, fourth bore 66 also is larger in diameter thancable 18 to accommodate second light beam 58. Third lens 60 may bedisposed in third bore 64 to collimate second light beam 58 before itcontacts second photodetector 54. In the case where third lens 60 onlycollimates second light beam 58, second photodetector 54 is larger indiameter than cable 18 so that cable 18 never fully shadows secondphotodetector 54 from second light beam 58. Second photodetector 54 maybe smaller in diameter than cable 18 when third lens 60 is a collectionlens larger in diameter than cable 18. As a collection lens, third lens60 focuses second light beam 58 onto second photodetector 54 wheresecond photodetector 54 detects changes in focused second light beam 58.Because second photodetector 54 or third lens 60 must be larger indiameter than cable 18 to prevent cable 18 from fully shadowing secondphotodetector 54 from second light beam 58, third bore 64 also is largerthan cable 18 to accommodate second photodetector 54 and third lens 60.

Second light beam 58 is orthogonal to first light beam 32 and mayintersect first light beam 32. First light source 30, first light beam32, and first photodetector are aligned and define an x-axis forlocating cable 18 within opening 26 of fleet angle sensor 20. Secondlight source 56, second light beam 58, and second photodetector 54 arealigned and define a y-axis for locating cable 18 within opening 26 offleet angle sensor 20. The z-axis of fleet angle sensor 20 is thedirection parallel to the center axis of fleet angle sensor and cable 18is parallel with the z-axis when the fleet angle of cable 18 is zero, asshown in FIG. 4. Because first photodetector 28 is aligned with thex-axis and faces orthogonal with the y-axis, first photodetector 28detects the position of cable 18 on the y-axis. Conversely, becausesecond photodetector 54 is aligned with the y-axis and faces orthogonalwith the x-axis, second photodetector 54 detects the position of cable18 on the x-axis. First light beam 32 and second light beam 58 are eachat least twice as large in diameter as cable 18. Because first lightbeam 32 and second light beam 58 are much larger in diameter than cable18, first light beam 32 and second light beam 58 together generallyencompass the full range of movement of cable 18 on an x-axis-y-axisplane within opening 26. Because first light beam 32 and second lightbeam 58 are each at least twice as large in diameter as cable 18, firstphotodetector 28 and second photodetector 54 may each be at least twiceas large in diameter as cable 18. Similarly, first lens 34, second lens36, third lens 60, and fourth lens 62 may each be at least twice aslarge in diameter as cable 18.

To determine the fleet angle of cable 18, fleet angle sensor 20 mustfirst detect a first set of x, y, and z coordinates of cable 18 relativeto a second set of x, y, and z coordinates of cable 18. Because sheaves22 center cable 18 above fleet angle sensor 20, as discussed above withreference to FIG. 2, it is known that the position of cable 18 atsheaves 22 has a fixed position with a y-coordinate set to zero, anx-coordinate set to zero, and a z-coordinate set to a known non-zerovalue. Because the position of first photodetector 28 and secondphotodetector 54 along the z-axis inside fleet angle sensor 20 is alsofixed and known, the second z-coordinate of cable 18 is known and fixed.Therefore, to find the fleet angle of cable 18, fleet angle sensor 20only needs to detect a y-coordinate and an x-coordinate of cable 18 onthe x-axis-y-axis plane that intersects the second z-coordinate of cable18 inside opening 26 of fleet angle sensor 20. As discussed below withreference to FIGS. 5A-5C, first photodetector 28 detects they-coordinate of cable 18 inside fleet angle sensor 20.

FIGS. 5A-5C will now be discussed concurrently. FIG. 5A is a front viewof first photodetector 28 from fleet angle sensor 20 of FIG. 4 and cable18 with a fleet angle of zero. FIGS. 5B and 5C are front views of firstphotodetector 28 from FIG. 5A and cable 18 with a fleet angle greaterthan zero. As shown in FIGS. 5A-5C, first photodetector 28 includesmultiple light-receiving zones designated as quadrant 1a, quadrant 2a,quadrant 3a, and quadrant 4a.

As discussed above with reference to FIG. 2, first photodetector 28 maybe a quadrant photodiode. First photodetector 28 may be circular withquadrant 1a, quadrant 2a, quadrant 3a, and quadrant 4a arranged suchthat quadrant 1a forms the northeast quadrant of first photodetector 28,quadrant 2a forms the northwest quadrant of first photodetector 28,quadrant 3a forms the southwest quadrant of first photodetector 28, andquadrant 4a forms the southeast quadrant of first photodetector 28. Asmall gap aligned with the y-axis separates quadrants 1a and 2a fromquadrants 3a and 4a. A small gap aligned with the z-axis and the centerline of fleet angle sensor 20 separates quadrant 1a from quadrant 2a,and also separates quadrant 3a from quadrant 4a. When no other forceother than gravity acts upon cable 18, cable 18 is aligned betweenquadrant 1a and 2a, and between quadrant 3a and 4a, and firstphotodetector 28 detects that the position of cable 18 on the y-axis isat zero. As shown in FIG. 5B, should cable 18 swing left relative thez-axis, cable 18 partially shadows quadrants 2a and 3a while quadrants1a and 4a are fully exposed. As described in greater detail in FIG. 7,first photodetector 28 determines a coordinate of cable 18 on the y-axisbetween quadrants 2a and 3a by comparing a signal generated by quadrant1a to a signal generated by quadrant 2a, and also by comparing a signalgenerated by quadrant 4a to a signal generated by quadrant 3a. As shownin FIG. 5C, should cable 18 swing right relative the z-axis, cable 18partially shadows quadrants 1a and 4a while quadrants 2a and 3a arefully exposed. As described in greater detail in FIG. 7, firstphotodetector 28 determines a coordinate of cable 18 on the y-axisbetween quadrants 1a and 4a by comparing a signal generated by quadrant1a to a signal generated by quadrant 2a, and also by comparing a signalgenerated by quadrant 4a to a signal generated by quadrant 3a. Asdiscussed below with reference to FIGS. 6A-6C, second photodetector 54detects the x-coordinate of cable 18 inside fleet angle sensor 20.

FIGS. 6A-6C will now be discussed concurrently. FIG. 6A is a front viewof second photodetector 54 from fleet angle sensor 20 of FIG. 4 andcable 18 with a fleet angle of zero. FIGS. 6B and 6C are front views ofsecond photodetector 54 from FIG. 6A and cable 18 with a fleet anglegreater than zero. As shown in FIGS. 6A-6C, second photodetector 54includes multiple light-receiving zones designated as quadrant 1b,quadrant 2b, quadrant 3b, and quadrant 4b.

As discussed above with reference to FIG. 2, second photodetector 54 mayalso be a quadrant photodiode. Second photodetector 54 may be circularwith quadrant 1b, quadrant 2b, quadrant 3b, and quadrant 4b arrangedsuch that quadrant 1b forms the northeast quadrant of secondphotodetector 54, quadrant 2b forms the northwest quadrant of secondphotodetector 54, quadrant 3b forms the southwest quadrant of secondphotodetector 54, and quadrant 4b forms the southeast quadrant of secondphotodetector 54. A small gap aligned with the x-axis separatesquadrants 1b and 2b from quadrants 3b and 4b. A small gap aligned withthe z-axis and the center line of fleet angle sensor 20 separatesquadrant 1b from quadrant 2b, and also separates quadrant 3b fromquadrant 4b. When no other force other than gravity acts upon cable 18,cable 18 is aligned between quadrant 1b and 2b, and between quadrant 3band 4b, and second photodetector 54 detects that the position of cable18 on the x-axis is at zero. As shown in FIG. 6B, should cable 18 swingleft relative the z-axis, cable 18 partially shadows quadrants 2b and 3bwhile quadrants 1b and 4b are fully exposed. As described in greaterdetail in FIG. 8, second photodetector 54 determines the coordinate ofcable 18 on the x-axis between quadrants 2b and 3b by comparing a signalgenerated by quadrant 1b to a signal generated by quadrant 2b, and alsoby comparing a signal generated by quadrant 4b to a signal generated byquadrant 3b. As shown in FIG. 6C, should cable 18 swing right relativethe z-axis, cable 18 partially shadows quadrants 1b and 4b whilequadrants 2b and 3b are fully exposed. As described in greater detail inFIG. 8, second photodetector 54 determines the coordinate of cable 18 onthe x-axis between quadrants 1b and 4b by comparing a signal generatedby quadrant 1b to a signal generated by quadrant 2b, and also bycomparing a signal generated by quadrant 4b to a signal generated byquadrant 3b.

FIG. 7 is a schematic diagram of first photodetector 28 from FIG. 5A andfirst circuit 68 associated with first photodetector 28. As shown inFIG. 7, first photodetector 28 includes multiple light-receiving zonesdesignated as quadrant 1a, quadrant 2a, quadrant 3a, and quadrant 4a.First circuit 68 includes first differential amplifier 70, seconddifferential amplifier 72, third differential amplifier 74, fourthdifferential amplifier 76, first summing amplifier 78, second summingamplifier 80, first output 82, and second output 84.

First differential amplifier 70 is electrically connected to quadrants1a and 2a and receives a signal from quadrant 1a and a signal fromquadrant 2a. First differential amplifier 70 compares the signal fromquadrant 2a to the signal from quadrant 1a by taking the difference ofthe two signals. First differential amplifier 70 outputs the differencebetween the signals from quadrants 1a and 2a to first summing amplifier78. Second differential amplifier 72 is electrically connected toquadrants 3a and 4a and receives a signal from quadrant 3a and a signalfrom quadrant 4a. Second differential amplifier 72 compares the signalfrom quadrant 3a to the signal from quadrant 4a by taking the differenceof the two signals. Second differential amplifier 72 also outputs thedifference between the signals from quadrants 3a and 4a to first summingamplifier 78. First summing amplifier 78 adds the outputs of firstdifferential amplifier 70 and second differential amplifier 72 to obtainfirst output 82, first output 82 being equal to the y-coordinate ofcable 18 on the y-axis. First output 82 can be mathematicallycharacterized by the following equation: First Output 82=y-coordinate ofcable 18=(1a+4a)−(2a+3a), where 1a is the signal from quadrant 1a, 2a isthe signal from quadrant 2a, 3a is the signal from quadrant 3a, and 4ais the signal from quadrant 4a.

Third differential amplifier 74 is electrically connected to quadrants2a and 3a and receives a signal from quadrant 2a and a signal fromquadrant 3a. Third differential amplifier 74 compares the signal fromquadrant 2a to the signal from quadrant 3a by taking the difference ofthe two signals. Third differential amplifier 74 outputs the differencebetween the signals from quadrants 2a and 3a to second summing amplifier80. Fourth differential amplifier 76 is electrically connected toquadrants 1a and 4a and receives a signal from quadrant 1a and a signalfrom quadrant 4a. Fourth differential amplifier 76 compares the signalfrom quadrant 1a to the signal from quadrant 4a by taking the differenceof the two signals. Fourth differential amplifier 76 also outputs thedifference between the signals from quadrants 1a and 4a to secondsumming amplifier 80. Second summing amplifier 80 adds the outputs ofthird differential amplifier 74 and fourth differential amplifier 76 toobtain second output 84. Second output 84 is equal to the z-coordinateof cable 18 on the z-axis. Second output 84 can be mathematicallycharacterized by the following equation: Second Output 84=z-coordinateof cable 18=(1a+2a)−(3a+4a), where 1a is the signal from quadrant 1a, 2ais the signal from quadrant 2a, 3a is the signal from quadrant 3a, and4a is the signal from quadrant 4a. As discussed above in the descriptionof FIGS. 3 and 4, the z-coordinate of cable 18 inside fleet angle sensor20 is generally fixed and does not change, thus second output 84 willlargely remain unchanged as cable 18 moves from side to side. Secondoutput 84 may be used to normalize first output 82 so as to minimizecommon mode errors in first output 82. Common mode errors in firstoutput 82 can result from stray light entering fleet angle sensor 20,temperature changes, or dust accumulating on lenses 34 and 36 disclosedin FIG. 2. First output 82 may be normalized by second output 84 bydividing first output 82 by second output 84. Normalized first output 82can be characterized mathematically by the following equation:Normalized First Output 82=[(1a+4a)−(2a+3a)]/[(1a+2a)−(3a+4a)], where 1ais the signal from quadrant 1a, 2a is the signal from quadrant 2a, 3a isthe signal from quadrant 3a, and 4a is the signal from quadrant 4a. Asdisclosed in FIG. 8 below, second photodetector 54 is connected tosecond circuit 86 in a manner similar to first photodetector 28 andfirst circuit 68.

FIG. 8 is a schematic diagram of second photodetector 54 from FIG. 6Aand second circuit 86 associated with second photodetector 54. As shownin FIG. 8, second photodetector 54 includes multiple light-receivingzones designated as quadrant 1b, quadrant 2b, quadrant 3b, and quadrant4b. Second circuit 86 includes first differential amplifier 88, seconddifferential amplifier 90, third differential amplifier 92, fourthdifferential amplifier 94, first summing amplifier 96, second summingamplifier 98, first output 100, and second output 102.

First differential amplifier 88 is electrically connected to quadrants1b and 2b and receives a signal from quadrant 1b and a signal fromquadrant 2b. First differential amplifier 88 compares the signal fromquadrant 2b to the signal from quadrant 1b by taking the difference ofthe two signals. First differential amplifier 88 outputs the differencebetween the signals from quadrants 1b and 2b to first summing amplifier96. Second differential amplifier 90 is electrically connected toquadrants 3b and 4b and receives a signal from quadrant 3b and a signalfrom quadrant 4b. Second differential amplifier 90 compares the signalfrom quadrant 3b to the signal from quadrant 4b by taking the differenceof the two signals. Second differential amplifier 90 also outputs thedifference between the signals from quadrants 3b and 4b to first summingamplifier 96. First summing amplifier 96 adds the outputs of firstdifferential amplifier 88 and second differential amplifier 90 to obtainfirst output 100, first output 100 equaling the x-coordinate of cable 18on the x-axis. First output 100 can be mathematically characterized bythe following equation: First Output 100=x-coordinate of cable18=(1b+4b)−(2b+3b), where 1b is the signal from quadrant 1b, 2b is thesignal from quadrant 2b, 3b is the signal from quadrant 3b, and 4b isthe signal from quadrant 4b.

Third differential amplifier 92 is electrically connected to quadrants2b and 3b and receives a signal from quadrant 2b and a signal fromquadrant 3b. Third differential amplifier 92 compares the signal fromquadrant 2b to the signal from quadrant 3b by taking the difference ofthe two signals. Third differential amplifier 92 outputs the differencebetween the signals from quadrants 2b and 3b to second summing amplifier98. Fourth differential amplifier 94 is electrically connected toquadrants 1b and 4b and receives a signal from quadrant 1b and a signalfrom quadrant 4b. Fourth differential amplifier 94 compares the signalfrom quadrant 1b to the signal from quadrant 4b by taking the differenceof the two signals. Fourth differential amplifier 94 also outputs thedifference between the signals from quadrants 1b and 4b to secondsumming amplifier 98. Second summing amplifier 98 adds the outputs ofthird differential amplifier 92 and fourth differential amplifier 94 toobtain second output 102. Second output 102 is equal to the z-coordinateof cable 18 on the z-axis. Second output 102 can be mathematicallycharacterized by the following equation: Second Output 102=z-coordinateof cable 18=(1b+2b)−(3b+4b), where 1b is the signal from quadrant 1b, 2bis the signal from quadrant 2b, 3b is the signal from quadrant 3b, and4b is the signal from quadrant 4b. As discussed above in the descriptionof FIGS. 3 and 4, the z-coordinate of cable 18 inside fleet angle sensor20 is generally fixed and does not change, thus second output 102 willlargely remain unchanged as cable 18 moves from side to side. Secondoutput 102 may be used to normalize first output 100 so as to minimizecommon mode errors in first output 100. As discussed above in thedescription of FIG. 7, common mode errors in first output 100 can resultfrom stray light entering fleet angle sensor 20, temperature changes, ordust accumulating on lenses 60 and 62 disclosed in FIG. 4. First output100 may be normalized by second output 102 by dividing first output 100by second output 102. Normalized first output 100 can be characterizedmathematically by the following equation: Normalized First Output100=[(1b+4b)−(2b+3b)]/[(1b+2b)−(3b+4b)], where 1b is the signal fromquadrant 1b, 2b is the signal from quadrant 2b, 3b is the signal fromquadrant 3b, and 4b is the signal from quadrant 4b.

In view of the foregoing description, it will be recognized that thepresent disclosure provides numerous advantages and benefits. Forexample, the present disclosure provides fleet angle sensor 20 formeasuring the fleet angle of cable 18 of winch assembly 12. Fleet anglesensor 20 includes first photodetector 28 and second photodetector 54.First photodetector 28 is a quadrant photodiode, and secondphotodetector 54 is a quadrant photodiode. As quadrant photodiodes,first photodetector 28 and second photodetector 54 are able toaccurately measure the fleet angle of cable 18 with a degree ofresolution and an extremely fast response time. It is estimated thatfleet angle sensor 20 is able to measure the fleet angle of cable 18within a tenth of a degree. Furthermore, fleet angle sensor 20 is alsorelatively small and simple in design, giving fleet angle sensor 20 asmall profile on winch assembly 12.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Forexample, while the specification describes frame 24 as an annular ring,frame 24 could be rectangular in geometry. Additionally, while firstphotodetector 28 and second photodetector 54 have been described in thespecification as each having four quadrants, first photodetector 28 andsecond photodetector 54 may have as few as two light-receiving zones orlight-active sectors. First photodetector 28 and second photodector 54,while described as quadrant photodiodes by the specification, couldinclude any kind of light-receiving device or plurality oflight-receiving devices arrayed into multiple light-receiving zones. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. An assembly comprising: a winch; a cable; and a fleet angle sensorcomprising: a frame disposed around an opening; a first photodetectorwith multiple light-receiving zones mounted on the frame; and a firstlight source mounted on the frame opposite the first photodetector; andwherein the first light source directs a first light beam across theopening to the multiple light-receiving zones of the firstphotodetector, the cable extends through the opening and into the firstlight beam, and the multiple light-receiving zones produce signals thatvary based upon a fleet angle of the cable extending through theopening.
 2. The assembly of claim 1, wherein the fleet angle sensorfurther comprises: a second photodetector with multiple light-receivingzones mounted on the frame; a second light source mounted on the frameopposite the second photodetector; and wherein the second light sourcedirects a second light beam across the opening to the multiplelight-receiving zones of the second photodetector, the cable extendsthrough the opening and into the second light beam, and the multiplelight-receiving zones of the second photodetector detect changes in thesecond light beam.
 3. The assembly of claim 2, wherein the firstphotodetector comprises four light-receiving zones arranged inquadrants.
 4. The assembly of claim 2, wherein the second photodetectorcomprises four light-receiving zones arranged in quadrants.
 5. Theassembly of claim 2, wherein the first photodetector is a quadrantphotodiode and the second photodetector is a quadrant photodiode.
 6. Theassembly of claim 2, wherein the first photodetector and the secondphotodetector are each larger in diameter than the cable.
 7. Theassembly of claim 2, wherein the first light beam and the second lightbeam are each larger in diameter than the cable.
 8. The assembly ofclaim 2, wherein the frame is an annular ring with an outercircumferential surface, an inner circumferential surface, and a topsurface opposite a bottom surface.
 9. The assembly of claim 2, whereinthe inner circumferential surface is several times larger in diameterthan the cable.
 10. The assembly of claim 2, wherein a shield device isdisposed under the frame to protect the sensor from the environment ordebris carried by the cable.
 11. The assembly of claim 10, wherein theframe further comprises: a first bore extending through the outercircumferential surface and the inner circumferential surface; a secondbore extending through the outer circumferential surface and the innercircumferential surface opposite the first bore and diametricallyaligned with the first bore; a third bore extending through the outercircumferential surface and the inner circumferential surface; a fourthbore extending through the outer circumferential surface and the innercircumferential surface opposite the third bore and diametricallyaligned with the third bore; and wherein the third bore and the fourthbore are circumferentially positioned ninety degrees from the first boreand the second bore.
 12. The assembly of claim 11, wherein the firstphotodetector is disposed on the outer circumferential surface over thefirst bore and the first light source is disposed on the outercircumferential surface over the second bore.
 13. The assembly of claim11, wherein the second photodetector is disposed on the outercircumferential surface over the third bore and the second light sourceis disposed on the outer circumferential surface over the fourth bore.14. The assembly of claim 13, wherein a first lens is disposed in thefirst bore, a second lens is disposed in the second bore, a third lensis disposed in the third bore, and a fourth lens is disposed in thefourth bore.
 15. The assembly of claim 14, wherein the first lens andthe third lens are collection lenses, and the second lens and the fourthlens are projection lenses, each lens being at least twice as large indiameter as the cable.
 16. A method for measuring the fleet angle of acable, the method comprising: directing a first light beam across anopening to a first photodetector with a first light-receiving zone and asecond light receiving zone; passing a cable through the opening andacross a portion of the first light beam; measuring the light receivedby the first light-receiving zone and the light received by the secondlight-receiving zone; and comparing a light measurement of the firstlight-receiving zone to a light measurement of the secondlight-receiving zone to calculate a first coordinate of the cable. 17.The method of claim 16, wherein the method further comprises: directinga second light beam across the opening to the second photodetector witha first light-receiving zone and a second light receiving zone; passingthe cable through the opening and across a portion of the second lightbeam; measuring the light received by the first light-receiving zone ofthe second photodetector and the light received by the secondlight-receiving zone of the second photodetector; and comparing a lightmeasurement of the first light-receiving zone of the secondphotodetector to a light measurement of the second light-receiving zoneof the second photodetector to calculate a second coordinate of thecable.
 18. An angle sensor comprising: a frame; a first light sourcedisposed on the frame; a first quadrant photodiode disposed on the frameopposite the first light source; a second light source disposed on theframe; a second quadrant photodiode disposed on the frame opposite thesecond light source; and a circuit for determining angular orientationof a cable passing through the frame based on signals from the first andsecond quadrant photodiodes.
 19. The angle sensor of claim 18, whereinthe first light source is circumferentially positioned on the framenonparallel from the second light source, and the first quadrantphotodiode is circumferentially positioned on the frame nonparallel fromthe second quadrant photodiode.
 20. The angle sensor of claim 18,wherein the first light source and the second light source are selectedfrom the group comprising lasers, LEDs, diode lasers, infrared emitters,ultraviolet emitters, and incandescent bulbs.